ALEXAJSTDEB TON HUMBOLDT. 81 climate on the plains of Chilpanteingo and Tasco, lying abotit 6000 or 7000 toises* above the level of the sea, and whose rich silver mines he visited; thence their journey lay over Cuernaraca, and through the fog exhalations of Guchilaquo to the beautiful town of Mexico. As the longitude of this place had, down to that time, been incorrect on the common maps, Humboldt rectified it by accurate astronomic calculations. But tlie antiquities especially occupied him here, and the statistics of the population. Having borrowed instru- ments for the purpose of the astronomic measure- ments above-named, from the excellent mining1 academy of Mexico, whose director was also a pupil of Werner, in Freiburg, he extended his inquiries to the celebrated mines of Moran and Real del Monte, and their environs, whence he returned in July, 1803, to proceed to the northern, districts of the country. He surveyed the artificial breach in the mountain Smog, near Desague cle Huehuctoca, which had cost six millions of piasters, and was intended to conduct the waters from the valley of Mexico ; he then repaired, by way of Salamanca, to the celebrated mining town. Guaiiaxuato, where he devoted two months to geognostic studies, especially to the detec- tion of ores, and then travelled through the valley of San, Tago, soixthwards to Vallaclolid, the capital of the ancient kingdom of Mechocart The rainy season did not deter the bold, and in the interest of science, indefatigable man from descending with his friend to the coasts of the Pacific, into the plains of the Jorullo, where, in the plain Malpais, in 1759, a considerable volcano had sprung uj> in one night, whose 2000 craters were still smoking, and were examined at considerable risk by Bonpland and Humboldt, who descended 250 feet into the burning crater of the central volcanic cone, on fragile lava pieces. To these .investigations, science owes a new important increase of its tacts and revelations on the history of the OnŠ toiae Is equal to six feet.